In a single word, Shadoko, yes.
Yes, the fact that D&D was the first pen and paper RPG to go big, and went huge in the 1980s (though interestingly it has far more players and makes far more money now, but that’s quite recent), and D&D was combat-focused because it evolved directly from a wargame - Chain mail, and was initially merely a spin off from that.
None of the other early pen and paper RPGs had the same intensity of focus on combat. It was still typically the most mechanically complex bit, but they had tons of rules for social and exploration and investigation stuff, which D&D really only gradually acquired from 1975 to 2000.
More details later maybe but yes blaming D&D is correct.
Edit - if you compare D&D to slightly later contemporaries like Traveller (1977) or Runequest (1978) you can see a huge difference in approach. There were essentially two strands of early TT RPG, those which basically emulated D&D but tweaked it in some way (Tunnels and Trolls, Tekumel, Chivalry and Sorcery, etc.) and this other strand which was already on the way before D&D, which Traveller and Runequest are prime examples of. Neither game makes combat its beating heart, and both provide tons of actual rules for exploration, interaction, social situations and negotiations and so on. Runequest was particularly decades ahead of its time, and still appears modern now. Cult CRPG King of the Dragon Pass is based loosely on it. I should do another thread on the the stuff D&D has lead to in games, because it’s pretty huge.